1. Field of the Invention
The present invention relates to a light emission device having a first electrode, a second electrode, and a fluorescent body which are disposed on a substance that serves as an emitter.
2. Description of the Related Art
In recent years, light emission devices employing electron emitters have been used in various applications such as field emission displays (FEDs) and backlight units. The electron emitter has an anode electrode and a cathode electrode as a basic element. In an FED, a plurality of electron emitters are arranged in a two-dimensional array, and a plurality of fluorescent bodies are positioned in association with the respective electron emitters with a predetermined gap left therebetween.
Conventional electron emitters are disclosed in, for example, Japanese laid-open patent publication No. 1-311533, Japanese laid-open patent publication No. 7-147131, Japanese laid-open patent publication No. 2000-285801, Japanese patent publication No. 46-20944, and Japanese patent publication No. 44-26125. All of these disclosed electron emitters are disadvantageous in that since no dielectric body is employed in the emitter, a forming process or a micromachining process is required between facing electrodes, a high voltage needs to be applied to emit electrons, and a panel fabrication process is complex and entails a high panel fabrication cost.
It has been considered to make an emitter of a dielectric material. The emission of electrons from a dielectric material has been discussed in Yasuoka, Ishii “Pulsed electron source using a ferroelectric cathode”, J. Appl. Phys., Vol. 68, No. 5, p. 546–550 (1999), V. F. Puchkarev, G. A. Mesyats, “On the mechanism of emission from the ferroelectric ceramic cathode”, J. Appl. Phys., Vol. 78. No. 9, November 1995, p. 5633–5637, and H. Riege, Electron emission from ferroelectrics—a review”, Nucl. Instr. And Meth. A340, p. 80–89 (1994).
In the above light emission devices, electrons emitted from an electron emitter are accelerated by an electric field produced by a collector electrode, and applied through a vacuum atmosphere to a fluorescent body, which is excited to emit fluorescent light. Since the distance that the accelerated electrons travel (flying distance) is very large, the accelerated electrons tend to collide with gas molecules that are present in the vacuum atmosphere. Therefore, it is difficult to supply electrons stably from the electron emitter to the fluorescent body. As the flying distance of accelerated electrons is very large, the light emission device cannot be reduced in size.
A spacer is often provided between the electron emitter and the collector electrode for keeping the gap between the electron emitter and the collector electrode at a predetermined distance and also for achieving desired rigidity of the light emission device. However, some of the accelerated electrons are liable to hit the spacer, negatively charging the spacer. When the spacer is negatively charged, a field distribution between the electron emitter and the collector electrode, i.e., a field distribution for directing electrons emitted from the electron emitter toward the collector electrode, is changed, so that the fluorescent body will not be excited accurately by the electron beam, tending to cause image quality failures and crosstalk.
Another problem is that positive ions generated by a plasma in the vacuum atmosphere impinge upon the cathode electrode, damaging the cathode electrode in a so-called ion bombardment phenomenon.
In the conventional light emission device described above, electrons restrained by the surface of the dielectric material, the interface between the dielectric material and an upper electrode, and a defective level in the dielectric material are emitted by a reversal of the polarization of the dielectric material. Stated otherwise, if the polarization of the dielectric material is reversed, the number of emitted electrons becomes substantially constant independently of the voltage level of an applied voltage pulse.
However, the conventional light emission device is disadvantageous in that it is not practical as its electron emission is not stable and it can emit electrons as many times as several ten thousands at most.